G proteins transduce extracellular signals, detected by cell surface receptors for hormones or sensory stimuli, into cellular responses mediated by altered function of effector molecules (enzymes or ion channels). This laboratory recently discovered the first two examples - gsp and gip2 - of a new family of oncogenes, created by activating mutations in the genes that encode the Alpha chains of Gs and Gi2, respectively. GSP oncogenes have been found in pituitary somatotroph tumors and thyroid tumors, and gip2 oncogenes in tumors of the adrenal cortex and in sex cord stromal tumors of the ovary. Our proposed experiments are designed to answer two complementary questions: 1. Which G protein Alpha subunits stimulate which intracellular signaling pathway? 2. Which Alpha chain genes may become oncogenes, and how do their protein products stimulate cell proliferation and tumorigenesis? We shall approach the first question with a strategy based upon cell- specific Expression of mutationally activated Alpha chains (carrying mutations identified in gsp and gip2) in appropriate cells. These experiments will identify the specific G protein Alpha chains responsible for inhibiting accumulation of cyclic AMP and for stimulating phospholipases in cultured cells, and those that regulate insulin secretion in B cells of the endocrine pancreas of transgenic mice. We shall approach the second question by studying effects of gip2 and other putative Alpha chain oncogenes (i.e., mutant proteins with activating mutations) on proliferation of cultured cells and on tumorigenesis in vivo. We will also survey human tumors for oncogenic mutations in genes for nine additional G protein Alpha chains, using the strategy (probing PCR-amplified tumor DNA with allele-specific oligonucleotides) that successfully identified gsp and gip2 oncogenes. This work will enhance our knowledge of how G proteins transduce specific signals, with special emphasis on those signals that regulate proliferation of normal and malignant cells.